OUString::replaceAt() does not replace in-place

Showed up as a warning: "ignoring return value of function declared with
warn_unused_result attribute". Please, use --enable-werror.

Change-Id: I783db186f0525df528174276958cce04ab9d44e8

sw/source/ui/uiview/srcview.cxx

@@ -207,7 +207,7 @@ static OUString lcl_ConvertTabsToSpaces( OUString sLine )
             }
             // Not 4 blanks, but on 4th TabPos:
             const sal_Int32 nPadLen = 4 - (nPos % 4);
-            sLine.replaceAt(nPos, 1, OUString(aPadSpaces, nPadLen));
+            sLine = sLine.replaceAt(nPos, 1, OUString(aPadSpaces, nPadLen));
             nPos += nPadLen;
         }
     }